1. Field of the Invention
This invention relates to the problem of delivering a combustible mixture of fuel and air to an internal combustion engine or other combustion appliance. It also relates to the problem of cooling a supercharge.
2. Background Art
Conventional carburetors and fuel injectors for internal combustion engines, as well as for other appliances, generate a heterogenous two phase product which consists of a liquid fuel phase and a gaseous combustion air phase. The incomplete mixing of the fuel and air leads to inefficient combustion, fuel wastage, and unnecessary pollution. Estimates vary, but some say up to 40-50% of fuel is wasted because of incomplete combustion. Vapor phase carburetors have been invented which attempt to deal with this problem by generating a molecular vapor from the liquid fuel before it is introduced into the combustion chamber. If a molecular vapor can be generated safely and effectively, and delivered to the combustion chamber in controlled dosages, essentially complete fuel combustion can be achieved, and much greater fuel economy can be achieved. However, it takes a tremendous amount of heat to vaporize traditional liquid fuels for internal combustion engines. For instance, a 235 horsepower engine at full load requires 10,486 watts of heat just to vaporize the fuel if liquid hexane is used as the fuel, assuming the liquid hexane is at or just below the liquid-gas phase change temperature just prior to vaporization.
The majority of the prior art vapor carburetion schemes seek to heat up the liquid fuel directly by surrounding the liquid fuel with a heating means or surrounding the heating means with a reservoir of liquid fuel, or by placing the heating means adjacent to the liquid fuel. The three main heating means employed in vaporizing fuel delivery systems are (1) heat supplied by the engine's exhaust system; (2) heat supplied by the engine's cooling system; and (3) heat supplied by electrical resistance heaters. Examples of devices using the engine's exhaust system as the heat source are the inventions of Zankowski (U.S. Pat. No. 2,800,533) and Budnicki (U.S. Pat. No. 4,476,840). An example of devices using the engine's cooling system as the heat source are the inventions of Ogle (U.S. Pat. No. 4,177,779). An example of a device using an electrical resistance heater as the heat source is the invention of Shih (U.S. Pat. No. 3,851,633).
In theory, it is acceptable to use electrical resistance heaters in such schemes because while in absolute terms the amount of heat necessary to turn the liquid fuel into vapor is quite high (viz., 10,486 watts) the relative amount is fairly low, say only about 2-40% of the gross engine output power. In other words, if the electrical resistance vaporization scheme adds a 40% fuel efficiency by giving the engine the opportunity to burn a homogeneous molecular vapor instead of a crudely mixed aerosol, then one can live with the 2-40% parasitic electrical generation load required. A further reason to use electrical resistance heating is that such a heating means is precisely controllable by carefully controlling the current through the heating circuit (Joule's Law). However, in some cases, the added parasitic load inefficiency, compounded by further inefficiencies in the belt, pulley, and bearing losses from the generator, make a significant operating cost difference. Furthermore the use of electrical resistance heating necessitates the cost and weight of expensive, heavy electrical generators and wiring harnesses; and is unsafe due to the hazard of electrical sparks and short-circuits developing in close proximity to the combustible mixtures.
Since there are already two sources of waste heat present in most internal combustion engines, the exhaust gases and the circulating coolant, an object of a more perfectly finessed invention is to rely on one of these already-present sources of heat rather than adding others. Both of these two sources have the added advantage that the available heat increases with the engine's demand for fuel on a roughly linear basis. The problem with using exhaust gases, however, is that it is extremely unsafe to put exhaust gases in close proximity to gasoline and combustible volatile mixtures. The closer the exhaust gas heat source and the thinner the partition between the exhaust gas stream and the gasoline, the better the heat transfer to the gasoline and the more efficient the vaporization process; but the more dangerous the situation can be should the partition fail and some of the hot, still-burning pieces of carbon and microscopic metal fragments enter into the gasoline.
One particular sub-class of vapor carburetor schemes which relies on the engine's circulating coolant to supply the heat necessary for vaporization is represented by the device of Ogle (U.S. Pat. No. 4,177,779) which relies on a large radiator placed inside the car's main fuel tank. The basic problem with devices of this sub class are safety and reliability. One sees that if Ogle dispenses with the car's “regular” radiator and goes only with a radiator in the gas tank, approximately ⅓ of the engine's heat would be supplied to the gas tank, whereas only 2-4% would be needed for the fuel vaporization. There would thus be a significant excess of gasoline vapor produced over and above that needed for engine operation. The interior gas tank pressures would soon go beyond practical limits unless extremely heavy pressure vessels were constructed to obviate this problem. This extra weight would eliminate the increased fuel efficiency desired. Using smaller radiators only lessens this problem. Furthermore, as the tank is drawn down, the changing heat transfer characteristics of the embedded radiator and the remnant fuel would represent an additional layer of complexity as far as keeping the pressure steady.
A better solution is to use a smaller secondary reservoir which is always kept filled, together with a more perfectly-tailored radiating device, with a controlled coolant flow. But even then, control of the varying pressures associated with the head space gases which need to be siphoned off represents a thorny engineering problem. The fact that no commercially-available fuel delivery system exists today based on this idea is a testament to its inherent intractability.
Another problem encountered with vapor phase fuel delivery systems is the need to control the fuel/air ratio over a wide range to allow for various engine operating conditions. The perfect stoichemetric air to fuel ratio for gasoline is 15:1 by weight or approximately 60:1 by volume. However, in internal combustion engine designs for automobiles, it is necessary for the fuel delivery system to provide a richer fuel mix during accelerations (say, 12:1), and a leaner fuel mix during long-range highway cruising (say, 18:1). Furthermore, in the case of automobile-based internal combustion engines, and other engines which deal with rapidly changing load conditions, the fuel/air ratio demands of the engines can change extremely rapidly, often in a small fraction of a second (viz., 50 milliseconds). It is therefore desirable that a fuel delivery system be able to vary the fuel/air ratio rapidly.
Instead of heating up reservoirs of liquid fuel to accomplish the phase transition of the fuel from liquid to vapor, an alternative scheme is to greatly increase the evaporative surface area of the reservoir so that more vapor will be generated. To this end, several capillary action evaporative wick carburetion schemes have been proposed. However, existing state-of-the-art capillary action evaporative wick carburetor schemes rely on ambient temperature air supplies for volatilization and have proven to be extremely difficult to control. In other words, in some cases they deliver too fuel-rich a mixture, while in other cases they deliver too-lean a mixture. There is no regularity or predictability to their performance.
For instance, Pedersen (U.S. Pat. No. 5,564,399 and U.S. Pat. No. 5,384,074) discloses the use of capillary action evaporative wicks to disgorge fuel vapors to the combustion air supply, but no mention is made of using any type of thermal regulating means to prevent freeze-up, and thus to allow such carburetors to function for extended periods of time. Freeze-up occurs because using a capillary action evaporative wick carburetor means one is essentially running a refrigerator. If thermal regulating means, specifically warming up means of some type or another are not supplied, the capillary action evaporative wick and the associated liquid reservoir will soon cool down (i.e., within seconds) to such an extent that no further vapor will be produced and the carburetor will cease to function. The laminar air flows, and metering schemes Pedersen teaches all mask this underlying issue. No mention is made of a method to bring the appropriate amount of heat to the evaporative wicks of Pedersen which would safely and effectively guarantee the proper functioning of this device for an extended period of time.
It is obvious that schemes which teach the use of capillary action evaporative wicks but do not teach the incorporation of an integral thermal regulating means are not practical devices. Note that beyond the issue of incorporating a thermal regulating means in the first place to counter the evaporative cooling effect of such vapor-generating devices, no mention or discussion is made at all in any of the prior art with regard to how to do this, i.e., what specific approaches to use, or what the technical challenges would be. For instance, would it be better to heat up the gasoline before impregnating the wick with it? Should separate heating elements be placed inside each wick? Should the heat source be exhaust gas? How should the heat source be placed in intimate connection with the fuel to be vaporized? How do you prevent overheating, etc. None of these important technical issues have been addressed in the prior art.
It is an object of the present invention to improve upon existing vapor carburetion schemes and to provide a safe, reliable and effective thermal regulating means for capillary action evaporative wick carburetors to allow them to function for extended periods of time.
Another object of the invention is to provide a reliable method to supply a homogeneous charge with a variable fuel/air ratio to throttle-controlled engines wherein the mechanical throttle setting by itself determines the engine speed.
Another object of the invention is to supply a means to vary the fuel/air ratio which can readily be put under the program control of an intelligent control oriented processor or other such micro-controller that has control of overall engine functions, including spark advance, and electro-mechanical valve timing, so that the fuel/air ratio can be adjusted in concert with these other engine functions electronically to achieve maximum fuel economy and emissions performance.
Another object of the invention is to provide a means of cooling supercharged (or turbo-charged) air-streams after they have come from the supercharger (or turbo-charger) but before they reach the engine. Supercharging, or turbo-charging, is a way to increase the horsepower of an internal combustion engine by increasing the density of the charge admitted to the combustion chambers. To do so, either the exhaust gas stream, or a pulley, or an electric motor is used to supply the force necessary for a blower or compressor to compress the in-rushing combustion air supply before it reaches the engine. The problem with this scheme, however, as that as the air is compressed, the air is also heated up as a natural consequence of Boyle's Law. Thus a 100% efficient supercharger will heat up the air passing through it by approximately 71 degrees Fahrenheit over the ambient air temperature when an 8 psi boost pressure is achieved. This extra heat of the combustion air which is admitted to the combustion chamber decreases the volumetric efficiency of the engine, remains a problem for the engine's cooling system to dissipate, and can lead to unsafe, premature detonation of the fuel/air mixture in spark ignition engines. Therefore makers of superchargers, turbo-chargers, and fuel delivery systems for engines have sought ways to cool the combustion air stream prior to its being admitted into the engine. In general, this practice is known as “inter-cooling” in the industry.
The methods developed for inter-cooling in automotive and marine engine applications may be broadly categorized into two separate categories: those which use heat exchangers in which a large volume of cooler air is brought into intimate contact with the in-rushing combustion air supply in a heat exchanger to lower the temperature of the supercharge, or those in which large quantities of cool water are brought into intimate contact with the in-rushing combustion air supply in a heat exchanger to lower the temperature of the supercharge. In contradistinction, the present invention does not rely on a heat exchanger as such and represents an entirely new and novel method of cooling a supercharge which does not require the additional expense of a heat exchanger and the additional equipment to guide either water or air through the inter-cooler heat exchange system, or the added mechanical inefficiencies and energy wastage associated with doing so, and which furthermore allows the formation of combustible mixture with a variable fuel/air ratio (“charge”) in a natural and surprisingly efficient way.